Join shm_pair.info and .segment of Windows shm implementation

There is not much point in having two distinct file mappings; since the
info mapping is very small and of fixed size, we can put it at the
beginning of a single mapping.  Besides the obvious resource savings,
that also simplifies the error handling.

Closes GH-8648.

Author: cmb69

TSRM/tsrm_win32.c

@@ -69,10 +69,8 @@ static void tsrm_win32_dtor(tsrm_win32_globals *globals)
 
 	if (globals->shm) {
 		for (ptr = globals->shm; ptr < (globals->shm + globals->shm_size); ptr++) {
-			UnmapViewOfFile(ptr->addr);
-			CloseHandle(ptr->segment);
 			UnmapViewOfFile(ptr->descriptor);
-			CloseHandle(ptr->info);
+			CloseHandle(ptr->segment);
 		}
 		free(globals->shm);
 	}
@@ -610,26 +608,27 @@ TSRM_API int pclose(FILE *stream)
 }/*}}}*/
 
 #define SEGMENT_PREFIX "TSRM_SHM_SEGMENT:"
-#define DESCRIPTOR_PREFIX "TSRM_SHM_DESCRIPTOR:"
 #define INT_MIN_AS_STRING "-2147483648"
 
 TSRM_API int shmget(key_t key, size_t size, int flags)
 {/*{{{*/
 	shm_pair *shm;
-	char shm_segment[sizeof(SEGMENT_PREFIX INT_MIN_AS_STRING)], shm_info[sizeof(DESCRIPTOR_PREFIX INT_MIN_AS_STRING)];
+	char shm_segment[sizeof(SEGMENT_PREFIX INT_MIN_AS_STRING)];
 	HANDLE shm_handle = NULL, info_handle = NULL;
 	BOOL created = FALSE;
 
 	if (key != IPC_PRIVATE) {
 		snprintf(shm_segment, sizeof(shm_segment), SEGMENT_PREFIX "%d", key);
-		snprintf(shm_info, sizeof(shm_info), DESCRIPTOR_PREFIX "%d", key);
 
 		shm_handle  = OpenFileMapping(FILE_MAP_ALL_ACCESS, FALSE, shm_segment);
-		info_handle = OpenFileMapping(FILE_MAP_ALL_ACCESS, FALSE, shm_info);
 	}
 
-	if (!shm_handle && !info_handle) {
+	if (!shm_handle) {
 		if (flags & IPC_CREAT) {
+			if (size > SIZE_MAX - sizeof(shm->descriptor)) {
+				return -1;
+			}
+			size += sizeof(shm->descriptor);
 #if SIZEOF_SIZE_T == 8
 			DWORD high = size >> 32;
 			DWORD low = (DWORD)size;
@@ -638,39 +637,25 @@ TSRM_API int shmget(key_t key, size_t size, int flags)
 			DWORD low = size;
 #endif
 			shm_handle	= CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, high, low, key == IPC_PRIVATE ? NULL : shm_segment);
-			info_handle	= CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, sizeof(shm->descriptor), key == IPC_PRIVATE ? NULL : shm_info);
 			created		= TRUE;
 		}
-		if (!shm_handle || !info_handle) {
-			if (shm_handle) {
-				CloseHandle(shm_handle);
-			}
-			if (info_handle) {
-				CloseHandle(info_handle);
-			}
+		if (!shm_handle) {
 			return -1;
 		}
 	} else {
 		if (flags & IPC_EXCL) {
-			if (shm_handle) {
-				CloseHandle(shm_handle);
-			}
-			if (info_handle) {
-				CloseHandle(info_handle);
-			}
+			CloseHandle(shm_handle);
 			return -1;
 		}
 	}
 
 	shm = shm_get(key, NULL);
 	if (!shm) {
 		CloseHandle(shm_handle);
-		CloseHandle(info_handle);
 		return -1;
 	}
 	shm->segment = shm_handle;
-	shm->info	 = info_handle;
-	shm->descriptor = MapViewOfFileEx(shm->info, FILE_MAP_ALL_ACCESS, 0, 0, 0, NULL);
+	shm->descriptor = MapViewOfFileEx(shm->segment, FILE_MAP_ALL_ACCESS, 0, 0, 0, NULL);
 
 	if (NULL != shm->descriptor && created) {
 		shm->descriptor->shm_perm.key	= key;
@@ -691,7 +676,6 @@ TSRM_API int shmget(key_t key, size_t size, int flags)
 			CloseHandle(shm->segment);
 		}
 		UnmapViewOfFile(shm->descriptor);
-		CloseHandle(shm->info);
 		return -1;
 	}
 
@@ -706,7 +690,7 @@ TSRM_API void *shmat(int key, const void *shmaddr, int flags)
 		return (void*)-1;
 	}
 
-	shm->addr = MapViewOfFileEx(shm->segment, FILE_MAP_ALL_ACCESS, 0, 0, 0, NULL);
+	shm->addr = shm->descriptor + sizeof(shm->descriptor);
 
 	if (NULL == shm->addr) {
 		int err = GetLastError();
@@ -734,7 +718,7 @@ TSRM_API int shmdt(const void *shmaddr)
 	shm->descriptor->shm_lpid  = getpid();
 	shm->descriptor->shm_nattch--;
 
-	ret = UnmapViewOfFile(shm->addr) ? 0 : -1;
+	ret = 1;
 	if (!ret  && shm->descriptor->shm_nattch <= 0) {
 		ret = UnmapViewOfFile(shm->descriptor) ? 0 : -1;
 		shm->descriptor = NULL;

TSRM/tsrm_win32.h

@@ -50,7 +50,6 @@ typedef struct {
 
 typedef struct {
 	void	*addr;
-	HANDLE	info;
 	HANDLE	segment;
 	struct	shmid_ds	*descriptor;
 } shm_pair;